A 58-year-old male factory worker presents with progressive bilateral hearing loss over 15 years. He reports difficulty hearing high-pitched sounds and tinnitus. Otoscopy is normal. Pure tone audiometry shows bone conduction thresholds within normal limits (0–15 dB HL), while air conduction thresholds are elevated at 500 Hz (35 dB HL), 1000 Hz (40 dB HL), 2000 Hz (50 dB HL), 4000 Hz (65 dB HL), and 8000 Hz (60 dB HL). Speech discrimination is 70%. What is the most likely diagnosis?

Explanation

## Audiogram Interpretation: Noise-Induced Hearing Loss ### Key Findings **Air-bone gap:** Absent (air and bone conduction both elevated equally) **Pattern of hearing loss:** Sensorineural (bone conduction normal, air conduction elevated) **Frequency distribution:** Classic **4 kHz notch** with relative sparing at 8 kHz — pathognomonic for NIHL. The dip at 4 kHz (65 dB HL) is characteristic. **Bilateral symmetry:** Both ears affected equally, consistent with occupational exposure. ### High-Yield Features of NIHL | Feature | NIHL | Presbycusis | Otosclerosis | |---------|------|-------------|---------------| | **Frequency pattern** | 4 kHz notch | High-frequency sloping | Flat or low-frequency | | **Air-bone gap** | Absent | Absent | Present (conductive/mixed) | | **Bone conduction** | Normal | Elevated | Normal (early) | | **Tinnitus** | Common, high-pitched | Present | Less common | | **Etiology** | Loud noise exposure | Age-related | Stapes fixation | ### Clinical Pearl **Key Point:** The **4 kHz notch** is the acoustic signature of noise trauma. The cochlea is maximally sensitive to frequencies around 3–6 kHz; prolonged exposure to industrial noise (>85 dB) causes selective outer hair cell loss at this frequency band. Recovery at 8 kHz is typical as the cochlea becomes less sensitive at higher frequencies. **High-Yield:** NIHL is: - Bilateral and symmetric - Sensorineural (air-bone gap absent) - Progressive with continued exposure - Irreversible - Accompanied by tinnitus and speech discrimination loss (70% here is consistent) ### Why This Patient Has NIHL 1. **Occupational history:** 15-year factory exposure (classic NIHL timeline) 2. **Bilateral symmetry:** Excludes retrocochlear pathology 3. **Normal bone conduction:** Rules out conductive or mixed loss 4. **4 kHz dip:** Pathognomonic for noise trauma 5. **Reduced speech discrimination (70%):** Indicates cochlear damage, not just threshold shift [cite:Dhingra's ENT 8e Ch 9]